1. Field of the Invention
The present invention relates to a seal ring provided between a rotating portion and a fixed portion in a rotating machine of a steam turbine and the like.
2. Description of the Prior Art
In a rotating machine of a steam turbine and the like, there is provided a seal fin for sealing between a rotating portion and a fixed portion facing to the rotating portion, for example, between a rotating outer circumferential surface formed by a tip of a moving blade and a blade ring therefor or between an inner circumferential tip surface of a stationary blade and a rotor surface facing thereto, as well as there is provided a seal ring supporting the seal fin.
FIG. 3 is a conceptual view of a representative seal ring in the prior art. In FIG. 3, the seal ring is split into four pieces, upper, lower, right and left, in a circumferential direction thereof, as shown by split pieces 21a, 21b, 21c and 21d. The right and left split pieces 21c and 21d are supported by supporting members 23 and 24, respectively, such that the right and left split pieces 21c and 21d are fixed in the horizontal direction, but movable in the upward and downward directions. Between each of the split pieces 21a, 21b, 21c and 21d, there are interposed springs 22 for activating these split pieces in a parallel direction with a tangent of a rotating circumferential surface of the rotating portion. Thus, not only the split pieces 21c and 21d, but also the split pieces 21a and 21b are movable in the upward and downward directions.
In the prior art seal ring constructed as mentioned above, while spring forces of the springs 22 act in the parallel direction with the tangent of the rotating portion circumferential surface, that is, substantially in the rotating portion circumferential direction, the split pieces 21a, 21b, 21c and 21d of the seal ring move in the upward and downward directions, respectively. That is, while the steam turbine is in operation with load, a high temperature high pressure steam flows around an outer circumference of the seal ring, and by the influence of this steam flow, as well as by the load of its own weight, the seal ring moves up and down, which causes deviations between the spring force direction of the springs 22 and the moving direction of each of the split pieces 21a, 21b, 21c and 21d of the seal ring. Thus, there occurs what is called a skirmish phenomenon of the split pieces in which mutually opposing end faces of the adjacent split pieces 21a, 21b, 21c and 21d deviate from a predetermined locus of movement to make an unusual engagement with each other and a sticking (a phenomenon of mutual biting) of the split pieces is liable to occur.
If such a sticking occurs, a clearance between the rotating portion and the fixed portion becomes large enough to cause a leakage of fluid, such as steam, and there arises a problem of deterioration of the performance.
In view of the problem in the prior art, it is an object of the present invention to provide a steam turbine seal ring which removes the problem in the prior art by ensuring movements of each portion of the seal ring so as to prevent deterioration of the sealing performance.
In order to attain the object, the present invention provides a steam turbine seal ring that is split into a plurality of seal ring pieces, each having a split plane on a portion so split. Each of the pieces having a seal fin fit on an inner circumferential surface thereof and being slidable in upward and downward directions along the split plane. The seal ring comprises a plurality of springs, each interposed between mutually adjacent ones of the seal ring pieces, for activating the seal ring pieces in the upward and downward directions along the split plane and a plurality of seal ring guides, each engaging with one of the seal ring pieces, for guiding the seal ring pieces in the upward and downward directions.
That is, in the present invention, the seal ring is split into plural pieces along the upward and downward directional split planes and the springs interposed between each of the seal ring pieces activate the seal ring pieces to move slidably in the upward and downward directions along the split planes. In addition thereto, the seal ring guides for guiding the seal ring pieces likewise restrict the seal ring pieces so as to move in the upward and downward directions. Thus, by the construction in which the three factors of the moving direction of the seal ring pieces, the acting direction of the springs and the guiding direction of the seal ring guides coincide with each other, the seal ring pieces move accurately so as not to invite deterioration of the sealing performance and a best suitable seal ring apparatus can be obtained.
Also, the present invention provides a steam turbine seal ring as mentioned above, characterized in that the seal ring pieces include an upper seal ring piece and a lower seal ring piece. A plurality of springs are provided, each interposed between the upper seal ring piece and a portion of the seal ring guides engaging therewith or between the lower seal ring piece and a portion of the seal ring guides engaging therewith, for activating the upper and lower seal ring pieces in the upward and downward directions.
That is, in the present invention, the springs are interposed between the upper seal ring piece or the lower seal ring piece and the seal ring guides engaging therewith for activation in the upward and downward directions. The upper and lower seal ring pieces are thereby in a state restricted by the spring forces between the upper seal ring guides and the lower seal ring guides. When the steam turbine starts to operate with a load in this state, a high temperature, high pressure steam flows around the seal ring pieces to cause a differential pressure and also the seal ring""s pieces own weight add thereto, thereby the seal ring pieces tend to move toward the inner side thereof as they are in the state so restricted. Thus, the upper and lower seal ring pieces move toward the inner side thereof against the spring forces and clearances between the upper and lower seal fins provided on the inner circumferential surfaces of the upper and lower seal ring pieces and outer circumferential surface of the rotor corresponding thereto are made narrower so that steam leakage from the upper and lower seal fins is reduced sufficiently, which results in further enhancement of the sealing performance.